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Cambridge International Examinations
Cambridge International Advanced Subsidiary and Advanced Level
* 4 5 4 0 7 5 8 2 6 8 *
9700/21
BIOLOGY
Paper 2 Structured Questions AS
May/June 2015
1 hour 15 minutes
Candidates answer on the Question Paper.
No Additional Materials are required.
READ THESE INSTRUCTIONS FIRST
Write your Centre number, candidate number and name in the spaces at the top of the page.
Write in dark blue or black pen.
You may use an HB pencil for any diagrams or graphs.
Do not use staples, paper clips, glue or correction fluid.
DO NOT WRITE IN ANY BARCODES.
Answer all questions.
Electronic calculators may be used.
You may lose marks if you do not show your working or if you do not use appropriate units.
At the end of the examination, fasten all your work securely together.
The number of marks is given in brackets [ ] at the end of each question or part question.
This document consists of 16 printed pages.
DC (ST/JG) 95553/3
© UCLES 2015
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2
Answer all the questions.
1
A student investigated growth in the roots of broad bean, Vicia faba. The student cut sections of
the root tip of this plant and viewed them with a light microscope.
Fig. 1.1 is a photomicrograph of one of the sections. The cell labelled D is in interphase.
A
H
B
G
C
F
E
D
Fig. 1.1
(a) Complete the table below by:
•
naming the stages of mitosis in the correct sequence following interphase
•
identifying one example from the cells labelled A to H that is in each stage of mitosis that
you have named.
stage of mitosis
label from Fig. 1.1
[5]
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(b) In animal cells, centrioles are responsible for assembling microtubules to make the spindle at
the beginning of mitosis.
Describe the role of the spindle during mitosis.
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(c) State two roles of mitosis in plants and animals other than growth.
1 ................................................................................................................................................
2 ............................................................................................................................................[2]
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(d) V. faba is a legume. Roots of legumes often have swellings at intervals known as nodules.
Cells within the nodules contain nitrogen-fixing bacteria.
(i)
Explain the role of nitrogen fixation in the nitrogen cycle.
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(ii)
Farmers in some parts of the world grow legume crops together with cereal crops in the
same field. This is known as intercropping.
Explain how intercropping results in an increase in the yield of the cereals when the
legumes die.
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[Total: 14]
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2
Pathogens enter the body in a variety of ways, including through the gas exchange system. The
body has several defence mechanisms against the entry of pathogens and their spread throughout
the body.
Fig. 2.1 is an electron micrograph of a cross section of the lining of a bronchiole.
X
Y
Fig. 2.1
(a) (i)
Name tissue X and cell Y.
X ........................................................................................................................................
Y ....................................................................................................................................[2]
(ii)
With reference to the structures visible in Fig. 2.1, state three ways in which the lining of
the trachea, bronchus and bronchioles provides protection against the entry of bacterial
pathogens.
1 ........................................................................................................................................
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2 ........................................................................................................................................
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3 ........................................................................................................................................
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Fig. 2.2 shows part of the immune response to the first infection by a bacterial pathogen that has
entered the body through the lining of a bronchiole. J and K are stages in the immune response.
Key
antigen
J
bacterium
secretion of
cytokines
cytotoxic
T-lymphocyte
L
K
B-lymphocytes
helper
T-lymphocytes
Fig. 2.2
(b) (i)
State what is happening at stage J.
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(ii)
Explain the role of cell L at stage K in the immune response.
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(c) With reference to Fig. 2.2, explain how the response to a second infection by this bacterial
pathogen differs from the first.
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(d) There are various ways in which the effectiveness of immune responses can be reduced.
Suggest how each of the following reduces the effectiveness of an immune response.
(i)
The number of T-lymphocytes is reduced in a person with HIV/AIDS.
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(ii)
Some pathogens are covered in cell surface membranes from their host.
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(iii)
B-lymphocytes do not mature properly and do not recognise any antigens.
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[Total: 14]
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3
When a leaf is first formed it is described as a sink for carbohydrate. As the leaf continues to grow,
it starts to photosynthesise and becomes a source of carbohydrates and other assimilates.
Fig. 3.1 shows the changes that occur to the structure of plasmodesmata in the leaf as it grows.
cytoplasm
cell surface
membrane
middle lamella
cell wall
two simple
plasmodesmata
complex (branched)
plasmodesmata
Fig. 3.1
(a) Suggest the advantage of complex plasmodesmata between cells in leaves.
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(b) Assimilates are transported into phloem sieve tubes.
Explain how assimilates in phloem sieve tubes move from the veins in a mature leaf to sinks,
such as flowers and fruits, in the rest of the plant.
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[Total: 6]
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4
(a) Fig. 4.1 shows two ways in which enzymes interact with their substrates.
substrate
enzyme A
enzyme B
Fig. 4.1
Explain the difference between the two ways in which enzymes interact with their substrates
as shown in Fig. 4.1.
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(b) Carbonic anhydrase is an enzyme that is found in blood, liver and kidneys.
Fig. 4.2 shows a molecular model of this enzyme.
P
Q
Fig. 4.2
(i)
With reference to Fig. 4.2 and the parts labelled P and Q, explain the term secondary
structure.
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(ii)
Describe the role of carbonic anhydrase in the blood.
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5
Fig. 5.1 shows a diagram of the molecular structures of tristearin (a triglyceride) and
phosphatidylcholine (a phospholipid).
H CH3
H
C
N+ CH3
H
C
H CH3
O
O P
H
H
H
H
C
C
C
O
O
O
H
H
C OC OC O
H
H
O
C
C
C
O
O
H
O–
H
C OC O
tristearin
phosphatidylcholine
Fig. 5.1
(a) Table 5.1 shows a structural difference between the two molecules shown in Fig. 5.1.
Complete Table 5.1 with two further structural differences other than in numbers of different
types of atoms.
Table 5.1
structural feature
length of fatty acid chains
tristearin
all the same length
phosphatidylcholine
different lengths
[2]
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(b) Cells in the pancreas secrete enzymes, such as amylase and trypsin, into a duct.
The enzymes are packaged in vesicles so that they can be exported from these cells as
shown in Fig. 5.2.
enzymes
plasma membrane
cytoplasm
Fig. 5.2
With reference to Fig. 5.2, explain how enzymes that are secreted by cells in the pancreas
are packaged into vesicles and exported.
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(c) Water has many significant roles to play in cells and living organisms.
Complete Table 5.2 below by stating the property of water that allows each of the following to
take place.
Table 5.2
role of water
property of water
solvent for glucose and ions
movement in xylem
helps to decrease body
temperature in mammals
[3]
[Total: 9]
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6
Red blood cells are formed from cells called reticulocytes. Stem cells in the bone marrow produce
reticulocytes which differentiate into red blood cells. During differentiation haemoglobin is
produced.
Fig. 6.1 shows the structure of small sections of DNA and messenger RNA (mRNA) in the nucleus
of a reticulocyte during transcription.
adenine
5' O
P
O
P
–O
O
NH2
N
N
N
O
O
N
N
O
P
–O
N
O
O
N
O
O
O
N
NH
3'
O
OH
P
–O
O
O
N
O
O
NH
N
N
O–
O
NH2
P
N
N
O
O
O
N
H2N
O
O
P
O
N
N
O–
O
N
NH2
O
O
NH2
O
O
O
P
–O
–O
O
H2N
NH
N
OH
O
P
N
O
N
O
O
O
N
H2N
R
O
O–
P
N
N
O
O
HN
O
O
NH2
N
O
O
NH2
O
N
O
P
O
–O
O
O
–O
5' O
P
HN
Q
O
3'
O
O
O
O
OH
P
–O
N
N
O
O
O
O
N
O
O–
O
O
P
O
NH
3'
O
O
S
OH
5'
Fig. 6.1
(a) Name the bases P to S.
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(b) Describe the role of the mRNA molecule shown in Fig. 6.1.
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[Total: 7]
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© UCLES 2015
9700/21/M/J/15